For non-avx optims, this saves 8 movs.

before:
  1785 decicycles in ff_vp9_loop_filter_h_44_16_ssse3, 524129 runs, 159 skips
  3327 decicycles in ff_vp9_loop_filter_h_48_16_ssse3, 262116 runs, 28 skips
  2712 decicycles in ff_vp9_loop_filter_h_88_16_ssse3, 4193729 runs, 575 skips
  3237 decicycles in ff_vp9_loop_filter_h_84_16_ssse3, 524061 runs, 227 skips

after:
  1768 decicycles in ff_vp9_loop_filter_h_44_16_ssse3, 524062 runs, 226 skips
  3310 decicycles in ff_vp9_loop_filter_h_48_16_ssse3, 262107 runs, 37 skips
  2719 decicycles in ff_vp9_loop_filter_h_88_16_ssse3, 4193954 runs, 350 skips
  3184 decicycles in ff_vp9_loop_filter_h_84_16_ssse3, 524236 runs, 52 skips